Since the lithium-ion battery has been widely commercialized, due to advantages, such as a high energy density and a high power density, the lithium-ion battery is widely applied in portable electronic devices, such as laptops, cameras and mobile phones. However, as the design constantly updates and the integrated features increases, people present a higher requirement on the energy density of the lithium-ion battery.
In order to improve the energy density of the lithium-ion battery, one method is to use a negative active material with a high specific capacity per gram (such as silicon-carbon composite negative active material and alloy negative active material). However, these negative active materials with a high specific capacity per gram have low first coulombic efficiency, and cannot significantly improve the energy density of the lithium-ion battery. In order to overcome this deficiency, it is necessary to perform a lithium-rich treatment on the electrode plate of the lithium-ion battery.
Chinese patent document with an issuance publication No. CN1290209C issued on Dec. 13, 2006 discloses a method of mixing a lithium metal, a negative active material and a non-aqueous liquid to form a slurry, then coating the slurry on a currect collector and performing a drying process and obtaining a negative electrode plate. Although this method can obtain a lithium-rich negative electrode plate, however, after the lithium metal is intercalated (absorbed) by the negative active material, voids will be left at the position of the original lithium metal on the negative electrode plate, thereby increasing the contact resistance between particles of the negative electrode plate.
Chinese patent document published as No. CN102779975A on Nov. 14, 2012 discloses a method of filtrating lithium powder with a filter screen via vibration and electric field to spill the lithium powder on a surface of a negative electrode plate to form a lithium-rich layer. The above method is simple in process, the slurry is not needed to prepare, however, the production efficiency is relatively low, and the problem that the spilled lithium powders are not uniform easily arises in actual operation. Moreover, the lithium powder easily floats in the air, thereby resulting in a serious safety hazard. Also, the lithium powder is expensive in price, and the production cost is relatively high.
An international patent application published as No. WO96/27910A1 on Sep. 12, 1996 discloses a method of coating a layer of lithium sheet on a negative electrode plate to obtain a lithium-rich negative electrode plate. The thickness of the lithium sheet in the above method makes the lithium amount thereof much more than the needed lithium amount of the negative electrode plate, the extra lithium will result in a serious safety hazard on the lithium-ion battery, and the extra lithium will also result in a disadvantage on the thickness of the lithium-ion battery.
Japanese patent document published as No. JP2005038720A on Feb. 10, 2005 discloses a method of depositing a lithium metal layer on a surface of a negative electrode plate via a method of vacuum deposition. The operating of the above method needs to be performed under a high vacuum environment, the production efficiency is relatively low and the production cost is relatively high.